By the way, this article has a list of everything that counts as a base item:

Player base[valheim.fandom.com]

Random spawns (as well as Raid spawns, but not Spawner spawns) are prevented within 20 meters of any of these. Having three or more within 40 meters of you makes you eligible for a raid when the check is made (one of the raid types doesn't have that requirement but only occurs in two biomes [Mountains and Plains], check occurs every 46 minutes of play time, 20% chance of a raid occurring).